The present invention relates to recording/reproducing control of a magnetic disk unit and relates to a recording/reproducing method and an apparatus of a magnetic disk unit capable of reducing the recording/reproducing process time of data.
When a magnetic disk unit is connected to a host processor and used as a random access file, the access time is comapratively long, i.e., approximately 100 times as compared with the read/write processing. In general, therefore, the magnetic disk unit is not always connected to the host processor, but disconnected from the host processor after the magnetic disk unit has received a command from the host processor via a disk control unit. If the seek command is issued from the host processor, for example, the disk control unit DKC which has received this command controls the magnetic disk unit DKU. In addition, the disk control unit DKC also disconnects itself from the host processor and waits for the operation completion report. When this seek operation has been completed, the disk control unit DKC reports the seek operation completion to the host processor and connects the disk control unit DKC to the host processor again. From the host processor, the disk control unit DKC receives a command specifying a position on the predetermined track for the information to be recorded onto/reproduced from. This position on the track is generally called set sector. Upon receiving a command of this set sector, the disk control unit DKC disconnects itself form the host processor again and directs the magnetic disk unit to search the concerned set sector. After the magnetic disk unit DKU has found the concerned set sector, the disk control unit connects the host processor to the magnetic disk unit again to effect data recording/reproducing operation.
As the procedure for termianting the seek command processing and receiving the command of the set sector, the magnetic disk unit DKU configured as described above does not accept the next command unless the seek command has not been terminated. Therefore, it takes some time from the termination of the seek command processing until the accept of the set sector command. (The average of the seek time is 18 msec, and the average of the set sector processing time is approximately 8.4 msec. That is to say, the seek time is longer than the set sector processing time.) Accordingly, the conventional magnetic disk unit has a problem that the unnecessary command wait time is included in the whole processing time of the recording/reproducing operation.
In order to solve this problem, a technique for rapidly effecting the seek completion report was proposed in JP-A-No. 58-159166 laid open to the public on Sept. 17, 1983. It is now assumed that this technique is used and a magnetic head has approached a desired track. When the movement and positioning speed of the magnetic head has been lowered below a predetermined value, the seek completion report is earlier issued and the head position at the time of seek completion is predictively controlled on the basis of the moving speed without distinction of read/write operation.
The processing in accordance with the above described prior art after the magnetic head has been positioned is carried out on the assumption that a set sector processing command is supplied from the host processor without failure. In actual processing, however, there are cases where data is directly read out into an arbitrary location or an empty sector or data is directly written withotu receiving a processing command from the host processor after the above described seek command. In this case, a gap might be produced between the predicted head position and the desired track. Despite the fact that the magnetic head is not positioned on the desired track, read and write processing commands might be issued from the host processor. Since the recording/reproducing operation is thus attempted at a position other than the desired track, there is a posibility that a read error or a write error is caused.